It is a matter of course that piping has become facilities which are essential for factories in various industries such as chemical and fuel industries. Recently the piping has become familiar for the civic life due to the spread of water supply, gas and central cooling and heating. Many systems including mainly pipes such as heat exchanger and boiler have been used. However many accidents have occurred due to failures of pipes. Maintenance operation such as inspection, cleaning and repair of the piping has become an essential operation for security of the civic life as well as the security of industry.
The pipings which are laid above ground and can readily be removed can be subjected to visual appearance inspection and precise inspection using various inspection instruments. However there has not been an appropriate inspection method for the piping buried underground. Conditions within the piping and decrease in wall thickness have been inspected by inserting a miniature camera or ultrasonic thickness measuring apparatus and the like into the piping portion slightly exposed above the ground. However such a method has difficulties as shown in FIGS. 4A and 4B. When the size of an inspection instrument to be inserted into the pipe is slightly smaller than the inner diameter of a pipe 2, the inspection instrument and the like 1 can be moved to a given position Q by actuating a rod 3 secured to the inspection instrument 1 from a position P, at which the inspection instrument is inserted. The relative position of the inspection instrument with respect to the pipe is not largely changed during the movement of the instrument. Accordingly, a necessary operation can be carried out at a given position if the inspection instrument has been preliminarily aligned with the pipe on insertion of the instrument. However the size of the inspection instrument should be made much smaller than the inner diameter of the pipe for passing through a bent portion such as elbow as shown in FIG. 4B if there is a bent portion between a position R where inspection is needed and a position P. In order to move the instrument, a flexible rod 4 such as a flexible spiral tube should be used in lieu of rod 3. By doing so, the relative position of the inspection instrument with respect to the pipe is largely changed so that the instrument is brought into misalignment therewith. It is also impossible to correct the misalignment from an external position of the pipe. In fact it has been impossible to carry out inspection at such a portion by means of an inspection instrument.
The size of the inspection instrument should be slightly smaller than the inner diameter of the pipe even when there is no bent portion such as elbow along the length of the pipe as shown in FIG. 4A. The precise inspection has been impossible by using an inspection instrument which requires precise alignment within a pipe.